The present invention is directed to an inkless fingerprinting compound and method of making the same.
Although there are other methods of identifying individuals, it has become readily apparent that fingerprints provide a unique and absolute means of identification that does not require cooperation from the subject. Since fingerprints are archived they must be permanent and because they are often captured by an electronic camera, the preferred color of fingerprint images is black. Printer""s ink, which contains carbon pigmentation, meets the requirements of image permanency and color, but it tends to smear on paper, requires time to dry, soils the skin and equipment, is skill intensive and time consuming to use. While carbon based inks have been formulated with small amounts of carbon pigmentation to reduce the staining problem (U.S. Pat. No. 5,395,444 and U.S. Pat. No. 5,919,292), such inks are not completely stain free.
To remove some or all of the negative aspects the prior art carbon based inks, a considerable amount of effort has been directed to the development of inkless fingerprinting systems which do not rely on carbon particles to form an image of the fingerprint ridge pattern. Inkless technology has traditionally been defined as a color forming chemical reaction, between at least two reagents, that occurs at the time of fingerprint development. The chemical reaction between the two (or more) reagents provides a permanent perceivable colorant product representative of a fingerprint ridge pattern on the recording medium. Current technology dictates that the two reagents remain isolated from each other until the fingerprint is to be taken.
Typically a nonstaining first reagent is applied to a person""s fingertips and a second reagent, capable of reacting with the first reagent to produce the colorant product such as 8-hydroxyquinoline, is pre-applied to or inherent in the recording medium such as the paper or card receiving the print. The second reagent can also be inherent in the paper receiving the print. See U.S. Pat. No. 4,983,415. Also see U.S. Pat. Nos. 4,262,623 and 4,182,261, the contents of which are incorporated herein by reference.
While the state of the art inkless systems have achieved considerable commercial success, they have their own set of shortcomings in addition to the need for two separated reagents. U.S. Pat. No. 4,190,056 Tapper et al relates to a method of reacting iodide with starch added to a paper recording medium, which fails to produce a black image. U.S. Pat. No. 4,879,134 to Vassiliades et al, discloses a fingerprinting composition which utilizes a chromographic compound and a color developing compound in one solution. While the Vassiliades et al patent refers to the system as an inkless system it is more properly classified as a nonstaining system since as the patent points out the liquid vehicle for the composition xe2x80x9cis a solvent for said chromogenic compound and reaction productxe2x80x9d, i.e., the reagents react while in the solution, prior to being applied to the finger and paper substrate (Col. 2, lines 36-37). Furthermore, it is not apparent that the images produced by the method would be sufficiently permanent. Also, it is not believed that AFIS (Automatic Fingerprint Information System) scanners would be able to satisfactorily capture images produced using this method.
U.S. Pat. No. 4,699,077 to Meadows and Diamond relates to a method involving chemically treated paper, a method that necessitates the cost of custom coating paper and this coating has a limited shelf life and is degraded when exposed to light. U.S. Pat. No. 4,983,415 to Arndt et al relates to an inkless system in which the fingerprint is captured on a thermosensitive recording surface, but this surface is not available on paper suitable for fingerprint cards, it yellows in the presence of light, it can not be used on checks and other documents, and it is not as inexpensive as commonly available, ordinary paper. U.S. Pat. No. 4,262,623 to Smith III et al relates to a method of recording inkless impressions on plain paper. However, this invention is costly, the apparatus requires a source of high voltage electricity and is therefore limited in its scope of operations and the system requires a lengthy image development process which can emit an offensive odor.
There is a need for an inkless fingerprinting system which overcomes the disadvantage of the prior art inkless technology systems. To fulfill this need, I have developed a single inkless fingerprint compound, i.e., liquid, paste or soap (i.e., vicious liquid), which can be transferred from a self-dispensing pad, such as ceramic, plastic, etc., to a person""s fingerprint area and then to an ordinary paper recording medium. The system does not require the use of reagents maintained in separate locations thereby eliminating the conventional two step inkless system, i.e., one reagent to be transferred by the fingertip to the recording medium and a second reagent impregnated or inherent in the recording medium. Further, unlike the Vassiliades et al system the reagents while maintained in a single container or dispensing pad are not allowed to react until the fingerprint is taken. I have found that the compound of my invention, through its interaction with moisture from the skin and/or the recording medium, rapidly forms a permanent, substantially dry, smear resistant and nonstaining perceivable colorant product of the ridge pattern representing the person""s fingerprint.
In accordance with the present invention an inkless fingerprint compound for providing a permanent colorant product representing a person""s fingerprint when applied to the person""s fingerprint area and deposited onto a paper substrate includes a solvent, a color former, such as a transition metal salt compatible with the solvent, and a developer, such as 8-hydroxyquinoline and its derivatives, capable of reacting with the color former to form the colorant product. The compound further includes a sufficient amount of a chelating agent, such as a carboxylic acid, to substantially prevent the color former and developer from reacting while in solution to form the colorant product while permitting such reaction when the solution is applied to the finger of the person to be fingerprinted and deposited onto the paper substrate.
The inkless fingerprinting compound may be in the form of a liquid, paste or soap (i.e., viscous liquid) and may be dispersed via a conventional ink type pad made for example of ceramic or plastic or other material which does not react with the compounds ingredients. Examples of suitable dispensing pads are disclosed in U.S. Pat. Nos. 4,262,613, 4,182,261 and 6,027,556.
The following description is provided to enable persons skilled in the art to make and use the invention and sets forth the best mode contemplated by the inventor of carrying out his invention. Various modifications, however, will be apparent to those skilled in the art, since the generic principles of the present invention have been set forth herein specifically to provide a single inkless fingerprint compound which deposited onto an ordinary paper substrate by a person""s finger, palm or foot will form a permanent colorant product delineating the ridge pattern of the fingerprint area.
In accordance with the present invention an inkless fingerprint compound for forming an permanent, substantially dry, smear resistant and nonstaining perceivable colorant product representing the ridge pattern of a person""s fingerprint when applied to the person""s finger and deposited onto an ordinary paper substrate is prepared by mixing a color former, a developer and a chelating agent in a compatible solution such as an aqueous solution. Additional reagents may be added to the mixture as will be described. The principal reagents, i.e., the color former and developer, are maintained in equilibrium, i.e., substantially kept from reacting to form the colorant product while in solution, as a result of the tight bond between the chelating agent and the color former. The chelating agent serves as a blocking agent while the color former and the developer are in solution in a container or self-dispensing pad while permitting the reagents to react when applied to a person""s finger (or other portions of the body) and subsequently deposited onto an ordinary paper substrate.
The color former may be one or more of the transition metal salts selected from the groups 5A-8A, 1B-5B and 7B of the periodic Table of Elements. More specifically while salts of iron, e.g., ferric chloride, have been found very satisfactory, salts of titanium, vanadium, chromium, magnesium, cobalt, nickel, copper, zirconium, zinc, niobium, molybdenum, silver, tantalum and tungsten have been found satisfactory.
The developer may be chosen from a group of reagents which form a colored reaction product with the chosen color former. While 8-quinolinol sulfate (developer) has been found to complex with ferric chloride (color former) to provide a permanent reaction product (black in color), other developers such as 2,4,6-Trihydroxy Benzoic Acid; 3,4,5-Trihydroxy Benzoic Acid; Dimenthyl Glyoxime; Rubeanic Acid; Pyrogallol; Hydroquinoline and its derivatives; Pyrocatechol; Propyl Gallate; Resorcinol; xcex2-Resorcylic Acid; Tiron (4,5-Dihydroxy-m-Benzene Disulfonic Acid Di-sodium Salt); Gentisic Acid; Procatechuic Acid; Phloroglucinol; and Tannic Acid and its derivatives have also been found to satisfactorily complex with one or more of the above color formers to provide perceivable colorant product representing a person""s fingerprint when deposited by the finger onto an ordinary paper substrate.
Developers, sometimes referred to as ionic binding developers, such as potassium ferrocyanide and sodium ferrocyanide and sulfide precursors such as sodium tetrathionate, sodium thiosulfate, diethyldithio carbamic acid, or 2-pyrrolidinecarbodithoic acid, may also be used. The resulting color, i.e., black, red, green etc. will depend upon the color former and developer used.
The chelating agent is an organic chemical capable of combining with (i.e., tightly binding with) heavy and alkali metal cations in the solution. I have found that a carboxylic acid, such as citric acid, when added to the transition metal salt in a sufficient quantity functions to block any substantial reaction between the color former and the developer until the fingerprinting procedure is initiated. The chelating agent may be bidentate, tridentate or tetradentate with 2, 3 or 4 sites, respectively, corresponding to number of donor atoms, (capable of sharing electrons) with election-deficient sites on metal ions, i.e., coordination sites. While there is an abundance of chelating agents or chelants capable of sequestering transition metal ions I have found that, among carboxylic acids, tartaric, suberic, succinic, malic, and axelaic acids with an electron donor site capability of xe2x88x922 are also suitable. Other chelants such as gluconates, polyacrylates, oxalates, and polyaspartates, sodium tripolyphosphate, aminopolycarboxylic acids, ethylenediaminetetracetic acid (EDTA) and nitrilotriacetic acid (NTA) and amines such as diethanolamine and triethanolamine will also serve the purpose. The preferred carboxylic acid is 2-hydroxy-1,2,3-propanetricarboxylic acid.
It is necessary to add a sufficient (e.g., stoichiometric) quantity of the chelating agent to the solution to sequester all or substantially all of the transition metal ions. Where the color former is a trivalent metal salt such as ferric chloride, with an ionic charge of +3 and the chelant is citric acid, with an electron-donor site capability of xe2x88x923, the molar ratio of the color former and chelant should be about equal, i.e., 1:1. Adding citric acid in a molar ratio greater than the moiety, i.e., 1:1, will drive the equilibrium of the chemistry more strongly toward the formation of ferric citrate in the solution. When this is done, to prevent any staining of the skin by the color forming reaction, the development of the colorant product on the paper substrate is retarded. It is possible to find a balance between the development speed of the image on the paper substrate and the cleanliness of the inkless solution on the skin. It is to be noted that whatever chelant and color former are used the molar ratio of chelant to color former must be such as to substantially sequester all of the metal irons. For example, when a chelant with an electron donor site capability of xe2x88x922, such as tartaric acid, is used with a trivalent metallic salt, such as ferric chloride, a molar ratio of at least 3:2 of acid to salt is needed to fully sequester all of the metal ions.
The following formulations of an inkless fingerprinting compound are examples only and not to be considered as limiting the scope of the present invention.